Method of manufacturing a drafting triangle

ABSTRACT

A METHOD OF MANUFACTURING A DRAFTING TRIANGLE FROM ACRYLIC SHEET PLASTIC BY SAWING A TRIANGLE PIECE OF PREDETERMINED SIZE FROM A PLASTIC SHEET, MILLING THE SIDES TO PROVIDE SQUARE GUIDING SURFACES AND CUTTING THE EDGES AT APPROXIMATELY A 45* ANGLE TO THE TOP AND BOTTOM TRIANGLE SURFACES AT A DEPTH OF APPROXIMATELY .005 OF AN INCH.

Jan.19,1971 .G. S.DOLGQ'RUKOV 3,555,651

METHOD OF MANUFACTURING A DRAFTING TRIANGLE Original Filed Dec. 19, 1963 v I 2 Sheets-Sheet 1 INVENTOR.

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Jan. 19, 19711 METHOD OF Original Filed Dec. 19, 19

63 2 Sheets-Sheet 2 INVENTOR.

United States Patent U.S. Cl. 29-407 5 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing a drafting triangle from acrylic sheet plastic by sawing a triangular piece of predetermined size from a plastic sheet, milling the sides to provide square guiding surfaces and cutting the edges at approximately a 45 angle to the top and bottom triangle surfaces at a depth of approximately .005 of an inch.

The present application is a division of my co-pending application, Ser. No. 331,800, filed Dec. 19, 1963, now U.S. Pat. No. 3,375,589 issued April 2, 196 8, for Drafting Instrument.

This invention relates to methods of making drafting instruments and more particularly but not exclusively to methods of making improved drafting triangles.

One of the difficulties in the use of drafting triangles results from the necessity of picking up the triangle for the purpose of moving it on the drawing, such as removing it from the ink line and/ or turning it over. The thickness of a drafting triangle being usually from to 35 does not provide a convenient finger hold thereon, and therefore ink lines are often smeared and considerable inconvenience to the user is otherwise caused in attempts to raise the triangle from the drawing.

It has been attempted to solve this problem by providing so-called finger lifts or beveling notches of the segmental shape with three of such notches usually provided on one surface of the triangle body and two or three on the other. It has been found, however, that such finger lifts are not fully operative for the intended purposes since they recess the body thickness only through very short distance and at their middle portions at that. The user would actually have to have a long nail on his thumb with which to get under the triangle at such short thumb recesses, which is not fully practicable.

It has been attempted to solve this problem by providing so-called continuous finger lifts, or, in effect, beveling the inner sides of the triangle from both top and bottom surfaces thereof to provide a virtually sharp edge. It has been found, however, that while such expedient operates satisfactorily while the triangle is new, as time goes on and the beveling becomes smooth, such expedient actually interferes with getting proper hold on the triangle for lifting. Another difficulty with drafting triangles was found in their susceptibility to breakage of their corners, nicking of their shap edges, particularly when plastic material such as transparent acrylic sheeting is used. This disadvantage has been usually charged to the physical properties of the material used rather than to the construction of the triangles. Particularly greater hardness and brittleness of the acrylic plastic as compared with other materials has been given as an explanation. Such an understanding induced recently a wire use of softer plastic for drafting triangles. However, use of less brittle but softer vinyl plastics did not solve the difficulty of nicking, since the edges of such triangles, while not brittle, are so soft that they can be easily nicked with ones nail; since their weak corners easily bend in fall, precision of such triangles is easily destroyed. In their prolonged use the middles of the Patented Jan. 19, 1971 ice guiding sides wear and cause formation of valleys therein.

In the search for greater transparency of such triangles and in the mistaken belief that highly polished surfaces are necessary therefor, resulting use of highly polished plastic sheeting made drafting triangles, by reflecting the windows and the overhead lights directly into draftsmens eyes, a source of eye strain cumulating through a period of years into injurious effect on draftsmens eyesight.

One of the objects of the present invention is to provide an improved drafting instrument such as drafting triangle whereby the above difficulties and disadvantages are overcome and largely eliminated without introducing other problems or appreciably increasing the costs involved.

Another object of the invention is to provide an improved drafting triangle which is more convenient to use and particularly is much easier to pick up from the drawing, and therefore is more efficient in use.

A further object of the present invention is to provide an improved drafting triangle which can be used for inking with the possibility of smearing wet inked lines being greatly reduced.

A still further object of the present invention is to provide a drafting triangle made of harder plastics and therefor presenting a harder edge but with the tendency of such edges and corners to nick, chip and break off, as observed in conventional triangles, being greatly reduced.

A still further object of the present invention is to provide an improved drafting triangle of the nature specified in the preceding paragraph in which nicking of the edges both caused by hitting hard objects as well as by formation of cracks, due to internal stresses or machining, is greatly reduced.

A still further object of the present invention is to provide an improved 45-9045 triangle including means provided therein for drawing 30-degree and 60-degree lines inclined in either direction.

A still further object of the present invention is to provide an improved triangle, the use of which greatly reduced general fatigue and eye strain.

Further objects and advantages of this invention will be apparent from the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification, wherein like reference characters designate corresponding parts in the several views.

FIG. 1 is an elevational view showing an improved 45- 45 triangle embodying the present invention.

FIG. 2 is a fragmentary sectional view taken in the direction of the arrows on the plane passing through the section line 2-2 of FIG. 1.

FIG. 3 is a fragmentary sectional view taken at the direction of the arrows on the section plane passing through the line 33 of FIG. 1.

FIG. 4 is an elevational view showing a 3090-60 drafting triangle embodying the present invention.

FIG. 5 is a fragmentary view showing on an enlarged scale the portion of the triangle of FIG. 4 encircled by the circle 5.

FIG. 6' is a fragmentary sectional view taken in the direction of the arrows on the section plane passed through the section line 66 of FIG. 4.

FIG. 7 is a view showing on an enlarged scale the corners of the triangle of FIG. 4, encircled in FIG. 4 by the circles 7.

FIG. 8 shows an improved 45 -90-45 triangle with provision therein to draw lines at 30 and 60 to the lines drawn along its guiding sides.

FIG. 9 is a diagrammatic view giving outline of the center aperture of the triangle of FIG. 8 and illustrating the angles formed by the inner guiding sides thereof.

bodiments and of being practiced or carried out in various Ways within the scope of the claims. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

In the drawings there are shown, by way of example, drafting triangles embodying the present invention. It is to be understood that the novel features of the constructions illustrated therein are represented graphically in a greatly exaggerated manner in order to permit making geometric constructions illustrating such features. Showing these features of construction to exact proportional scale would make the drawings impracticably large or the novel features of construction so small as not to be legible.

Referring specifically to FIGS. 1-3, the drafting triangle illustrated therein comprises a flat body genererally designated by the numeral 11 and having top and bottom surfaces and outer guiding sides 12, 13, and 14. The sides 12 and 13 form between them an angle of 90, and the third side or hypotenuse 14 makes the angles of 45 with sides 12 and 13, respectively. The guide sides are of a square cross section, as is best shown in FIG. 2, and are adapted to guide an instrument point, such as that of a pencil or an inking pen.

In the middle portion of the body 11 there is provided a triangular aperture having inner sides 15, 16, and 17, generally parallel to the outer guiding sides of the triangle body. The inner sides 15, 16, and 17 are not guiding sides, but are provided with a concave recess 20, 21, and 22, respectively, to impart to the inner sides a concave cross section such as illustrated in FIG. 2. The recesses are symmetrical with respect to the axis of the cross section in order to provide substantially sharp edges, such as edges 22a and 22b, substantially along the entire lengths of the respective inner sides and both along the top and bottom surfaces of the body. By virtue of such a construction the sharp edges provide a more effective hold for the users thumb, with such sharp edge being disposed twice as high from the drawing surface than is the case with beveling the inner sides from the top and bottom. Wearing out of the triangle affects such edges very little and therefore their effectiveness is preserved for many years.

In accordance with the invention, means are provided eliminating the possibility of origination of cracks and breakage of the triangle at the corners of the inner aperture. It has been found that drafting triangles usually break through their corners even if such corners have square cross sections. Presence of sharp edges such as 22a and 22b in the corner would promote such breakage and could, in effect, defeat advantages of the present invention.

In accordance with the present invention, the corners of the aperture are rounded as illustrated in the drawings. The rounded corners such as illustrated in the drawings may be formed by drilling them with ball or spherical mills with which the recesses are cut. By virtue of such a method, rounding of the corners and provision of recesses may be made in a single operation, such as by recessing the inner sides with a spherical milling cutter the elevation of which with respect to Work is adjusted to have its center on the axis of the body thickness, and thereupon sinking and withdrawing such cutter at each corner. Of course, these two operations may be performed in reversed order. Also, the corner holes may be drilled and relieved or chamfered at the edges in separate operations first, and thereupon the aperture may be cut out with square sides and recessed as explained above to provide the continuous concave finger lifts as explained. It is of importance that the sharp edges of the corners are relieved for a small distance, such as .010 as indicated at 25 in FIG. 3. By virtue of such an expedient breakage of the triangles at the corners are greatly reduced as compared With conventional triangles.

FIG. 4 shows a 30-90l60 triangle in which the continuous finger lifts are formed by cutting them in the inner sides of the triangle body at the aperture to extend further into the sides than do the corners of the aperture as illustrated in FIGS. 4 and 3 wherein such recesses are designated by the numerals 30, 31, and 32. In this construction the sharp edges of the body at the round corners of the aperture are also removed, as is best illustrated in FIGS. 5 and 6 wherein such relief on the corners is designated by the numerals 33 and 34. Since these corners are not guiding elements the precise depth of the relief is not critical and may be made larger.

The triangle illustrated in FIGS. l-3 as well as other triangles illustrated and described below are made of hard plastic to provide hard edges, and paritcularly from cast and annealed acrylic sheets, from which such triangles are cut by milling operations. While such material provides for hard guiding sides not susceptible of nicking by nail pressure and rapid wear causing bowing or caving in wear of the sides by the action the instrument points, the brittleness of such material makes their sharp edges susceptible to deterioration because of the formation of minute cracks at sharp edges in the process of milling. Such cracks rapidly grow inwardly of the body of the triangle and causing crumbling out of the material when two adjacent cracks meet. In addition, such edges are exceedingly susceptible of nicking by even by light impacts on hard objects, such as frames of the drawing boards should the triangle happen to fall down. It is well appreciated in the art that even a small nick on a triangle guiding side may cause the draftsman to discard the triangle as being a source of faulty work and extreme annoyance.

The sharp edges of the guiding sides along the top and bottom surfaces of the body 11 are cut away as indicated at 18 and 19 in FIG. 2. It is preferred to cut such edges to a uniform depth around the entire triangle for the depth of from .003" to .010", preferably at a 45 angle, thus making the exposed edges of the guiding sides forming the angles of 135 instead of The edges so produced may be polished, if desired. It should be under stood that the depth of such edge relief on guiding sides is critical and it should not affect squareness of the sides. Generally this relief, in spite of its critically important effect, is so small as to be invisible by the naked eye and its presence may not be realized by the triangle user.

By virtue of the above-described expedient the sharp edge in which minute cracks have been formed in milling are removed, and a single 90 edge is substituted by two edges, producing a hard and strong edge that has extremely long life, makes smearing of ink lines less likely and provides for more pleasant handling of the triangle. This expedient has a number of further important advantages.

FIG. 8 illustrates a 45 9045 triangle having outer guiding sides 40, 41, and 42 and a central aperture having inner guiding sides 43, 44, 45, 46 and 47. It is important to appreciate that in this particular triangle all five inner sides of the body at the inner aperture are guiding sides, i.e., are adapted to guide instrument points. It is also important to appreciate that while in the triangles of FIGS. 1 and 4 the sides of the inner opening are generally parallel to their respective outer guiding sides, in those constructions this relationship is not of a precision nature and such parallelism is sufficient if it satisfies the requirements of appearance. On the other hand in the triangle FIG. 8, the angular relationship of the inner sides with respect to the outer sides is a precision relationship.

Particularly, the inner side 43 is parallel to the outer guiding side 40 and perpendicular to the outer guiding side 41. The inner guiding side 44 is parallel to the outer guiding side 41 and is perpendicular to the outer guiding side 40. The inner guiding side 46 is parallel to the outer guiding side 42 and forms angles of 45 with sides 40 and 41. The inner side47 forms an angle of 60 with the outer guiding side 40, and a 30 angle with the outer guiding side 41. Also, the sides 45 and 47 make the angles of 105 and 75 with the sides 42 as illustrated. In addition, the guiding sides of the aperture make between themselves angles of 90, 120, and 105 as illustrated in FIG. 9. Thus, the angles most useable in an engineering drawing may be laid off with the use of the triangle of FIG. 8 without changing to a 3090-60 triangle or to a protractor. The inner angles of the aperture may be rounded on a radius such as A in order to produce a more durable triangle and to enable drawing rounded corners and fillets without the use of a compass.

An important advantage of all of the triangles illustrated herein lies in the provision of outer corners which resist chipping and breaking, an exceedingly objectionable occurrence frequently observed in conventional triangles.

It is important to appreciate that mere rounding such corners is not fully effective to eliminate such condition, and this fact proved very misleading to those skilled in the art. I have found that this results from the fact that triangles seldom fall remaining in a position perpendicular to the floor. In a fall, a triangle usually assumes an inclined position and hits the floor not with the rounded but with the sharp edge of the corner which sharp edge mere rounding of the corners does not eliminate. As a result of such fall, a large scale or piece of the plastic is broken off the corner, and the final result is usually the same as that which follows if a triangle hits the floor with a sharp or unrounded corner.

In accordance with the present invention the sharp edges at the rounded triangle corners are removed both at the top and bottom surfaces of the triangle as is best illustrated in FIG. 10, wherein the sharp corner 50 at which the two guiding sides meet is eliminated to provide a rounded surface 51. The sharp edges 52 and 53 formed by such rounding at the top and bottom surface of the triangle body are eliminated by angular cuts to provide surfaces such as illustrated at 54. Use of the designating numeral for a similar surface at the bottom of the triangle is avoided in FIG. to prevent confusion of the leader lines.

In accordance with the invention the radius on which rounding of the corners of the triangles are made is inversely proportional to the size of the angle, i.e., the larger is the angle the smaller is the radius on which such rounding is made. Since provision of the surface such as 54 depends in its size on the radius at which the corners are rounded, the same relationship remains with respect to provision of such surface. I prefer to provide such surfaces to approximately one-half of such circle as is best illustrated in FIG. 7, at an angle from to 50. Use of the straight cut is preferable as easily done, but use of curved cuts may be still more advantageous.

As illustrated in said FIG. 7, triangle shown therein has the largest radius at its corner, while the 90 corner has the smallest. Under some conditions, and particularly with smaller triangles, rounding of the 90 corner may be eliminated entirely. The size of the corner radii also depends on the size of the triangle. With the large triangle, such as those of 24" size, such radii are much greater than in the corresponding corners of small triangles. For instance, a 30 corner of a 24" triangle may have a radius of A while the same corner of an 8 triangle may have that radius equal to only Within the last 20 years or so tit; eye strain in drafting work increased at an alarming rate, producing severe headaches and nervous strain and causing inability of a draftsman to continue with drafting work and retirement several years earlier than before. Such condition prevailed in spite of the fact of presumably better lighting in drafting rooms.

I have v found that while the intensity of illumination did increase in general and in drafting rooms in particular, the lighting fixtures became very large, often being continuous from wall to wall of a drafting room and having considerable width. In addition, the windows in drafting rooms have also greatly increased in size. This made it impossible to eliminate reflection of such lighting fixtures, shining directly into draftsmens eyes from the reflecting surface of a drafting triangle, merely by slightly changing the working position as was possible to do with smaller round lights before the advent of the present-day fluorescent lighting fixtures.

Another difliculty resulting from such a condition is found in the necessity of straining draftsmens vision to distinguish a transparent edge of the drafting triangle, particularly those made of colorless acrylic plastic from the lines-on the drawings, particularly in operations such as section lining, in the performance of which the draftsman has to set an almost invisible edge of a drafting triangle from the thinnest line on the drawing. While old celluloid material had amber tint which became darker with age, acrylic plastic, a material of the highest transparency, remains colorless, greatly enhancing the eye strain problem. Attempts have been made to use color acrylic such as green or pink fluorescent, providing a clearly visible and distinguishable edge on the triangle. It has been observed, however, that such expedient was not only ineffective to relieve the eye strain but in many cases increased it. I have found that this condition resulted from providing a color contrast between the triangle body and the paper, which is also an injurious condition. Some draftsmen having particularly sensitive eyes see a complimentary color on the paper when using such color triangles.

In accordance with the present invention, the top surface of the drafting instruments such as triangles is made non-reflecting, such as providing a satin or frosted finish thereon. By virtue of such an expedient, reflections of overhead lights and windows are eliminated, thus relieving severe eye strain on draftsmens eyes.

It should be understood in providing the satin or frosted finish, that in cases of 45 -90-45 triangle such as shown in FIGS. 1 and 8, it is generally suflicient to provide such finish on one surface only and use the triangle to have its frosted or satin finish surface as the top surface. Such triangles need not be turned over to get all of the angles which may be set with such a triangle. 'On the other hand with 30-90-60 triangles, such as one shown in FIG. 4, it is necessary to provide the frosted or satin finish on both top and bottom surfaces thereof since it is necessary in use to turn such triangle over.

In addition, in accordance with the invention I eliminate use of the colors in a manner used before and use acrylic material of very light green or yellow color, in effect only faint light color tint, suflicient only to distinguish the edge of the triangle but not sufficient to give the color contrast of the objectionable nature. Triangles made of acrylic material a very light green tint proved to be of greater benefit to draftsmens eyesight and their working efliciency.

It will be understood that the guiding edges of all triangles illustrated herein are constructed as illustrated in FIG. 2 to eliminate the sharp edges and that all of the corners of the triangles may be constructed as illustrated in FIG. 7.

By virtue of the above-described constructions the objects of the present invention listed. above and numerous additional advantage are attained.

Iclaim:

1. In a method of manufacturing from acrylic plastic material a drafting triangle to provide milled guiding surfaces having line edges resistant to formation thereon of cracks and inward propagation thereof, the steps of providing a sheet of cast and annealed sheet acrylic plastic material of a predetermined thickness and having flat top and bottom surfaces, sawing a triangular piece of predetermined size from said sheet, milling sides of said triangular piece at predetermined angles to each other to provide square guiding surfaces having sharp line edges along said sides both at the top and bottom surfaces, and removing the sharp line edges formed in the process of milling by cutting the material at said sharp line edges at approximately 45 angle to said flat top and bottom surfaces and depth of approximately .005 of an inch to produce identical edges at the top and bottom surfaces and to provide for using the triangle selectively either at its top or its bottom surface.

2. In a method of manufacturing from acrylic plastic material a drafting triangle to provide milled guiding surfaces having line edges resistant to formation thereon of cracks and inward propagation thereof, the steps of providing a sheet of cast and annealed acrylic plastic material of a predetermined thickness and having flat top and bottom surfaces, sawing from said sheet a triangular piece of predetermined size, milling out a triangular aperture with rounded corners in said triangular piece to provide squared surfaces on said triangle all around said aperture, and thereupon removing the curved line edges both at the top and the bottom surfaces of said triangular piece in the corners of said aperture for approximately .0l of an inch at approximately 45 angles, milling sides of said triangular piece at predetermined angles to each other to provide square guiding surfaces having sharp line edges along said sides both at the top and bottom surfaces of the triangular piece formed in the process of milling, and removing said sharp line edges by cutting the material at said sharp line edges at approximately 45 angles to said flat top and bottom surfaces and depth of approximately .005 of an inch to produce identical edges along the squared guiding surfaces at the top and bottom surfaces and thus to provide for using the triangle selectively either at its top or its bottom surface.

3. In a method of manufacturing a drafting triangle, the steps of providing a sheet of cast and annealed acrylic plastic material of a predetermined thickness and having flat top and bottom surfaces, sawing from said sheet a triangular piece of predetermined size, milling out in said piece a triangular aperture with rounded corners to provide, first, squared surfaces on said triangular piece all around said aperture, and thereupon milling the straight portions ofsaid squared surfaces, but not the rounded corners thereof, with a circular cutter to provide concave arcuate recesses along said square surfaces along said aperture with the radius of the arc thereof being larger than the half of the thickness of the triangle, and with the arcuate surfaces of the recesses crossing the top and the bottom surfaces of the triangle to produce a substantially sharp picking up edge.

4. The method defined in claim 3, with the radius of the cross section of the recesses being smaller than the full thickness of the triangle but larger than half of the thickness thereof, whereby the flesh of the users thumb is made to enter the recesses to a sufficient degree forlpicking up the triangle Without the use of the thumb na1 5. The process defined in claim 3 with a step of drilling in said triangular piece round holes to form round cor ner in said aperture of a radius greater than the corners merging smoothly with the adjacent straight picking-up edges in said aperture, and to have the square walls of said holes come in substantial coincidence with the bottoms of the concaved recesses.

References Cited UNITED STATES PATENTS 2,428,699 10/ 1947 Ebert 331 10 3,398,449 8/ 1968 Dolgorukov 29407 2,562,348 7/1951 Bowser, Jr. 29407X JOHN F. CAMPBELL, Primary Examiner R. J. CRAIG, Assistant Examiner US. Cl. X.R. 33l04, 112 

